Seismic data acquisition and processing techniques are used to generate a profile (image) of a geophysical structure (subsurface) of the strata underlying the land surface or seafloor. Among other things, seismic data acquisition involves the generation of acoustic waves, the collection of reflected/refracted versions of those acoustic waves and processing the collected seismic data to generate the image. This image does not necessarily provide an accurate location for oil and gas reservoirs, but it may suggest, to those trained in the field, the presence or absence of oil and/or gas reservoirs. Thus, providing an improved image of the subsurface in a shorter period of time is an ongoing process in the field of seismic surveying.
Considering the improvement of seismic images, the determination of a velocity function is an important step in the processing of seismic data. The velocity function (or velocity model) is a mathematical representation of the speed of a wave through a medium, in this instance the speed of a seismic wave through the underlying ground strata. The velocity function is necessary for processing seismic data. The velocity function, once determined, can be used to convert a time domain velocity model to a depth domain velocity model, a domain capable of removing structural errors inherent in time migration. A velocity function can be computed by different techniques, e.g., a ray-tracing algorithm in conjunction with a time-to-depth conversion algorithm, but this, and other, techniques are computationally intensive and have other limitations associated with the accuracy of the velocity function over the seismic area of interest and the amount of data required to perform the analysis.
Moreover, the propagation velocity in a given medium is related to a particular physical property of the medium. In particular, the knowledge of both P-wave and S-wave velocity leads to a Poisson ratio of the medium. Accordingly, it would be desirable to provide systems and methods that avoid the afore-described problems and drawbacks, and provide methods to derive a velocity function which are more accurate and/or less computationally intensive.